sanguineus

Sanguine comes from Latin sanguineus (of blood, bloody), from sanguis (blood). In Galen's four-humor system, the sanguine temperament was associated with an excess of blood — the warm, wet humor. Sanguine people were cheerful, sociable, confident, and physically ruddy-complexioned. They laughed easily, loved company, and expected the best. Blood was the humor of spring, of youth, of air.

The medieval and Renaissance understanding of the sanguine temperament made it the most attractive of the four. Where the phlegmatic was sluggish, the choleric was angry, and the melancholic was depressed, the sanguine person was pleasant, hopeful, and good company. Chaucer's Franklin in the Canterbury Tales is described as sanguine — red-faced, pleasure-loving, and hospitable. The word was a compliment wrapped in a diagnosis.

The double meaning of sanguine — both 'optimistic' and 'bloody' — created a word that looks different depending on context. 'The battlefield was sanguine' means covered in blood. 'He was sanguine about the outcome' means he was optimistic. The two meanings share a root but point in opposite directions. Blood on the ground is horrifying. Blood in the body makes you cheerful. The word holds both truths.

Modern English has almost entirely abandoned the bloody meaning in favor of the optimistic one. 'Sanguine' now appears in newspaper editorials and business reporting: 'Markets remain sanguine about inflation.' The word has been cleaned of its blood. The optimism is all that survives.